MiL
Posts: 281
Joined: 1/22/2002
From: Bend,
OR, USA
Status: offline
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taking things pretty off topic from r/c engines, but...
I'm not quite sure what to make of the new GP1 motorcycle class. It was kind of cool to have the super exotic 500's all by themselves, and World Superbike to take care of the 4 strokes... then again, the lifting of homologation rules from the 4 strokes will allow for some outrageous things and probably accelerate the development of new technology for consumer sportbikes.
It seems to me that the only drawbacks to 4 strokes are weight and size. Not size as in displacement, because that's not really important, but rather size of the motor as a whole due to the much larger heads, etc. To make a 4 stroke motor with a given power output and under a certain weight, is generally much more complex and expensive than making a 2 stroke with the same power and weight specs.
Even among 4 strokes their are some motors that seem to behave more like what we expect of 4 strokes than others. For example inline 4 cylinder engines vs. v-twins.
I have a Yamaha R6, a 600cc inline-4 street bike. It doesn't even begin to make power untill about 8,000 rpm, and really comes alive around 10,000-14,500 rpm (at which point it is a rocketship). The motor makes right around 100 horsepower.
I've also ridden a Ducati 996 and a Honda RC51, both 1 liter V-twins. These motors seem much 'torquier' (sp?) and begin making (and also stop making) horsepower at significantly lower rpm. You don't have such a narrow window for power with these motors and they are resultingly easier to ride with and require less shifting. Again, like a 4 stroke vs. a 2 stroke, a v-twin requires a displacement advantage over a 4 cylinder in order to offer similar performance. In superbike, 1000cc twins are allowed to race against 750cc 4 cylinders. When first introduced, the twins were still at a power disadvantage. Now they have been developed to the point where they actually have an
advantage. in GP1 2 strokes of 500cc will be raced against 4 strokes of up to 990cc (i think). There are different displacement and weight restrictions imposed on different 4 stroke engine configurations (like v-twin, inline 3's or 4's, v-5 honda, etc.). The general consensus is that the power delivery of a twin makes for more useable and tractible power than that of a 4 cylinder, which in turn is more useable and tractible than that of a 2 stroke.
So in the end, it seems to be a bit of a toss-up and definitely there are a lot of trade-offs and compromises... such is life. My father told me that most everything in life is a trade-off. I've found this to be true very much of the time.
As far as model planes are concerned, i dont have nearly as much experience (my first 4 stroke is in the mail.. Saito .72), but from what i've been able to glean a 2 stroke will always offer the most power for the weight. Again, 4 strokes seem to make more 'useable' power, being able to swing larger, more efficient props. My guess would be that in any kind of performance oriented aircraft, untill you start getting to really large scale, a single cylinder engine is definitely the way to go, and most of the time, a 2 stroke will give best performance. But, like i said, i don't have much experience here yet and i may very well be off base.
Multi cylinder model plane engines i would think would be best used only in very large models, which are easily able to deal with the extra weight. Or in models for which all out performance is not as important.
Personally, i'm willing to throw on a little extra weight in trade (see  ) for a more aesthetically and aurally pleasing motor. I may not even give up much performance wise since this particular motor is fairly light weight for it's displacement.
Anyway, i've rambled on long enough...
< Message edited by MiL -- Mar 8 2002 8:53PM >
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Two-strokes VS Four-strokes -- Do I dare? - 
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